Known in the art is an extruder head for making anticorrosive tubular polymeric film (SU, A, 859178), comprising a body and a hollow core accommodated therein, the walls of the body and core defining a molding passage. An insert is mounted in the interior of the core coaxially therewith, the insert protruding from the end face of the core and having a passage for supplying compressed air laden with finely divided powder. The protruding portion of the insert has radial ports communicating with the passage. Polymer melt is supplied from the extruder to the molding passage of the extruder head and is blown at the outlet thereof with the aid of the compressed air laden with powder which is supplied from the core passage through the radial ports. The extruder head of this type cannot impart desired anticorrosive properties to the tubular film since a part of the powder is lost during application, and inhibition is non-uniform. In addition, saturation of the film with the pulverulent inhibitor is hampered because the inhibitor does not substantially diffuse into the body of the film and is only deposited on the surface.
Known in the art is an extruder head for making anticorrosive tubular polymeric film (SU, A, 722779), comprising a hollow body with an extrusion die, a core mounted in the body and extending through the extrusion die, the outer surface of the core defining with the inner surfaces of the body and extrusion die a molding passage terminating in an annular opening, circular grooves being provided in the zone of the opening in the body of the core and extrusion die which have their open sides facing towards each other and which receive liners made of a material permeable for a corrosion inhibitor or its solution in a plastisizer, the inner walls of the linear and the walls of the groove defining chambers. The body and the core are made with passages communicating with the chambers of the extrusion die and core, respectively, for supplying a liquid lubricant thereto, and a passage being provided in the body of the core for supplying compressed air for blowing polymer melt into a tube.
A liquid lubricant is supplied under pressure to the polymer melt fed from the extruder into the molding passage when it flows through the annular opening from the chambers of the extrusion die and core so as to form a uniform layer on the surface of the melt along the opening. The polymer melt supplied from the extruder is in the form of a mixture of a thermoplastic with a corrosion inhibitor.
The use of the lubricant ensures a reduction of coefficient of friction of thermoplastic melt with the opening walls and makes it possible to process heavily-filled thermoplastics. The liquid lubricant does not have any effect on the anticorrosive properties of the film. The tubular film made with the aid of the extruder head of this type does not have the desired complex of anticorrosive properties as corrosion inhibitor in encapsulated in the thermoplastic and its release into the body of the tube is hampered so that quality of the film is rather low.